/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import java.lang.reflect.Array;
import java.util.List;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;

/**
 * Methods factored out so that they can be emulated differently in GWT.
 * 
 * @author Hayward Chan
 */
@GwtCompatible(emulated = true)
class Platform {

    /**
     * Calls {@link List#subList(int, int)}. Factored out so that it can be
     * emulated in GWT.
     * 
     * <p>
     * This method is not supported in GWT yet. See <a href=
     * "http://code.google.com/p/google-web-toolkit/issues/detail?id=1791"> GWT
     * issue 1791</a>
     */
    @GwtIncompatible("List.subList")
    static <T> List<T> subList(List<T> list, int fromIndex, int toIndex) {
        return list.subList(fromIndex, toIndex);
    }

    /**
     * Calls {@link Class#isInstance(Object)}. Factored out so that it can be
     * emulated in GWT.
     */
    @GwtIncompatible("Class.isInstance")
    static boolean isInstance(Class<?> clazz, Object obj) {
        return clazz.isInstance(obj);
    }

    /**
     * Clone the given array using {@link Object#clone()}. It is factored out so
     * that it can be emulated in GWT.
     */
    static <T> T[] clone(T[] array) {
        return array.clone();
    }

    /**
     * Wrapper around {@link System#arraycopy} so that it can be emulated
     * correctly in GWT.
     * 
     * <p>
     * It is only intended for the case {@code src} and {@code dest} are
     * different. It also doesn't validate the types and indices.
     * 
     * <p>
     * As of GWT 2.0, The built-in {@link System#arraycopy} doesn't work in
     * general case. See
     * http://code.google.com/p/google-web-toolkit/issues/detail?id=3621 for
     * more details.
     */
    static void unsafeArrayCopy(Object[] src, int srcPos, Object[] dest,
            int destPos, int length) {
        System.arraycopy(src, srcPos, dest, destPos, length);
    }

    /**
     * Returns a new array of the given length with the specified component
     * type.
     * 
     * @param type
     *            the component type
     * @param length
     *            the length of the new array
     */
    @GwtIncompatible("Array.newInstance(Class, int)")
    @SuppressWarnings("unchecked")
    static <T> T[] newArray(Class<T> type, int length) {
        return (T[]) Array.newInstance(type, length);
    }

    /**
     * Returns a new array of the given length with the same type as a reference
     * array.
     * 
     * @param reference
     *            any array of the desired type
     * @param length
     *            the length of the new array
     */
    static <T> T[] newArray(T[] reference, int length) {
        Class<?> type = reference.getClass().getComponentType();

        // the cast is safe because
        // result.getClass() == reference.getClass().getComponentType()
        @SuppressWarnings("unchecked")
        T[] result = (T[]) Array.newInstance(type, length);
        return result;
    }

    /**
     * Configures the given map maker to use weak keys, if possible; does
     * nothing otherwise (i.e., in GWT). This is sometimes acceptable, when only
     * server-side code could generate enough volume that reclamation becomes
     * important.
     */
    static MapMaker tryWeakKeys(MapMaker mapMaker) {
        return mapMaker.weakKeys();
    }

    private Platform() {
    }
}
